Telephone-exchange system



Dec. 27., 1927. 1,653,789

R. L. STOKELY TELEPHdNE EXCHANGE SYSTEM Filed April 9, 1925 55 Sheets-Sheet 1 y GOMPOSWE RINGER m emor: R0] 1. Jmfey Dec. 27, 1927.

R. L- STQKELY TELEPHONE EXCHANGE SYSTEM Filed April 9. 1925 3 Sheets-Sheet 3 zgi M M QM MGM Patented Dec. 27, 1927.

UNITED STATES QPATENT OFFICE. I

BAY L. STOKE'LY, fill FLORAL FARE, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COIV IZPAINY, INCORPORATED, A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filedlApriI 9, 1925. Serial No. 21,756.

This invention relates to telephone systerns, and more particularly to improvements in circuit arrangements for enabling toll operators to build up toll connections to automatic subscrihcrslines.

A general object Of this invention is to improve the operating etliciency and to effect equipment economy in circuits of this character.

In present trunking systems of this type the toll lines incoming to a toll operators position, are either equipped with composite ringers or else merely arranged totransmit ordinary ringing current signals. in the first instance. the 1G cycle ringing current applied by the composite ringer to a toll operators cord circuit, is usually of such value as to cause disturbances in the circuits beyond it", for example, these signals are applied as a re-ringing signal to the toll operator when a cord circuit is connected through to an outgoing trunk leading to an automatic exchange, and the called subscriber has already been connected and has his receiver oil the hook. That is, this re-ringing signal may. in this case, operate the regular ring-up relay in the trunk circuit, and consequciuly cause the ringing relay to operate and apply ringing current to the called suh scrihcrs line. On the other hand, the ringup relay may operate in case the re-ringing signals from an ordinary toll line are un usually strong, which might be due either to disturbances on a particular line or to the Fact that the line itself is unusually short. ltgain, it the connected trunk line happens to be short. the incoming re-ringing signals from either of these two types of lines may be sulliciently strong to cause the ring-up relay to function.

llcretotore a special rin -up relay was used provided with a weighted arn'iature so arranged in relation to the contact springs of the relay that they Would not operate in response to incoming re-ringing signals; but, on the other hand, would operate satisfaci ly in i ponse to signaling current outgoing trom a toll operators cord circuit that manner for calling However. relays of ich the magnetic effect on directly proportional to the nt may not prove entirely 1 Pry under all circumstances as, for

ing signals outgoing from the toll operators position, are such as to barely operate the Weighted armature, in which case this armature would tend to fluctuate for a short interval before it finally settles down to positively operate the contacts. Such uncertain operation of the ringing equipment would consequently be unsatisfactory.

Another object of this invention is therefore to provide ringing equipment in trunk lines, outgoing from a toll operators position and terminating at automatic exchanges, that responds positively to ringing signals originating at a toll operators cord circuit and does not operate at all When reringing signals are applied to the operators cord circuit from either a toll line equipped with a composite ringer or an ordinary toll line. i

To accomplish these and other objects of the invention, there is provided in accordance with one feature thereof, a ring-up relay in the circuit arrangement, for the operation of the ringing relay, in which the ring-up relay is provided with two springs ct relatively ditierent stillness, the stiffer of these springs being arranged to complete an energizing circuit for the slow-release ringing relay and the other more flexible spring, which naturally will operate before and release after the stitler spring, is arranged to close a holding circuittor the ringing relay alter the original operation thereof. By means of this arrangement, it will be seen that any ringing signal that is of sulficient value to once operate the stiffer spring and cause the operation of the ringing relay,

will also cause the locking circuit for the ringing relay to be closed, and any subsequent fluctuations oil? the stiffer spring that might open the original energizing circuit Will not ordinarily cause the ringing relay to release, this being partly due to the slow release characteristics of the ringing relay itself but primarily due to the tendency of the more flexible spring of the ring-up relay to remain operated after the less flexible spring has released.

To further improve the efliciency of this usual type of ring-up relay, the toll lines and composite ringers may be so arranged that the 16 cycle ringing current maybe applied to the toll operators cord circuit at more accurate. and adjusted values. F or this purpose, compensating resistances may be included between the ringing source and the line, or the outputof the ringing source itself may be correspondingly adjusted.

Another feature of the invention resides in' the provision of means for further elimination of disagreeable clicks in a subscribers receiver connected to a trunk line when the ringing relay operates. To this end, use is made of what are called continuity springs on the ringing relay, i. e., by so arranging the contact springs on this relay that the ringing current will be connected to the subscribers line before the talking battery is disconnected therefrom, and vice versa.

1 To accomplish the general object of increasing the efliciency of circuits of this type, another feature of the invention resides in means for positively disconnecting the ringing current from a called snbscribers line the moment the subscriber lifts the receiver from the hook on answering a call, even though the ringing key at the toll operators position may still be operated thus entirely eliminating any possibility of the subscriber being annoyed by having to listen to the ringing after the receiver has been rcmoved. i a

Still another feature of the invention reside in the provisio'nof an arrangement for connector circuits for preventing a false advance of the brushes of a connector switch from the terminals of the lasttrunk line of a group of P. B. X. trunk lines to the ter minals of the first trunk line of the next succeeding group of trunks or of the next succeeding subscribers line in case this test trunk line is busy, that is, if a second connector switch is already connected therewith.

Other features will appear hereinafter.

Having described in a brief way the operation of the system embodying the present invention, a more detailed description will now be given in connection with the accompanying drawings in which:

Fig. 1 shows a toll operators cord circuit arranged inaccordance with this invention associatedwith two diiferent types of incoming toll lines; Fig. 2 shows an outgoing trunk circuit adapted for association with the cord circuit and an automatic selector switch. in which this trunk circuit termt nates at an automatic exchange; while Fig. 3 shows a connector circuit at this exchange and a called subscribers line.

hen pluglOO of the toll operators cord circuit is inserted in jack 101 of a ringdown toll line in response to the lighting 01 a line lamp (not shown), relay 102 operates in an obvious circuit. The operation of relay 1052 in turn operates relay 103, under control of relay 104. The operation of relay 103 prevents relay 105 from. operating and also the lighting of supervisory lamp 106. The. toll operator havin received the number of the desired line at her telephone set 150, which is connected to the cord circuitby operation of the talking key 151, touches the tip ot plug 107 to the sleeve of jack 200 (Fig. 2) to select an idle trunk line leading to the machine switching office in which the desired line terminates and if it is idle inserts the plug and operates the dialing key 11:).

A busy condition of the trunk line is indicated by battery on the sleeve of the jack 200, which produces a click in the receiver 108 0'1 theoperators telephone set 150 in the :t'ollowing manner: Battery on the sleeve, over the tip of the plug 107, outer leit normal contacts of relay 109, inner lei't normal con tacts of relay 110, through the left-hand winding of induction coil 112 to ground. Current in this circuit produces a click in the receiver 108 due to the flow of induced current in a circuit comprising the righthand winding of induction coil 112. the upper and lower normal contacts of relay 1.13 and the winding of receiver 108.

The insertion of the plug 107 in jack 200 combined with the operation of dialing key 115 causes the operation of relays 109 and 202, the circuit of which can be traced as follows: battery, outer normal contacts of relay 116, left-hand winding of relay .100, lowermost alternate contacts of key 115, outer left normal contacts of relay 110, ring contacts of plug .107 and jack 200, outer le'lt normal contacts of relay 201 and left-halal winding of relay 202 to ground. Relay 10!). in operating, disconnects the cord circuit from the plug and connects the dial circuit, including dial 118, thereto instead.

The operation of relays 109 and 202 completes a series circuit for the operation of relays 203 and 119 which can be traced as follows: battery, normal contact oi relay 120, winding of relay 1'19, right hand winding and right alternate contacts of relay 1051, sleeve contacts of the plug 107 and jack 200. left alternate contacts of relay 202 and righthand winding of relay 203 to ground. The operation of relay 119 closes an obvious circuit for relay 116 which then operates. thereby closing the dialing loop including the tip and ring of the plug through the contacts of dial 118. Relay 203, in operating connects battery at its left alternate con tacts to the winding of relay 901v thereby causing its operation. Relay 201, in operating, opens at its outer le-ft normal contacts the operating circuit for relay Q02 and closes at its contacts 205, a holdingcircuit for this same relay which can be traced from battery, left alternate contacts of relay 20 1, right-hand winding of relay 202, contacts 205, relay 201 and to ground through the left-hand winding of relay 202. Relay 201, in operating, also closes its innermost alternate contacts thereby partially closing a bridge including relay E200 across the trunk conductors. The circuit is not completed,

Ill!

however at this time as it is opened at the right-hand normal contacts of relay 203. Further, relay 201 in operating extends the trunk conductors to the distant otlice and also locks up at its contacts 207 under control of relay 206.

The combined operation of relays 109, 116 and 201 closes the trunk circuit including winding of pulsing relay 204211; the machine switching oflice. This circuit can be traced from battery, normal contacts oi: release magnet 208, right-hand winding of pulsing relay 109, tip contacts of the plug 107 and jack 200, contacts 220 of relay 201, contacts 218 of relay 212, resistance 262 and contacts 221 of relay 212 to ground. Relay 1 operates in this circuit but polarized relay 120 doesnotoperate at this time due to its connection in the circuit with respect to the polarity of the battery at the machine switching office.

The operation of relay 204:, closes at its right alternate contacts, an obvious circuit for operating relay 222. Relay 222, in operating, closes its right alternate contacts 227 thereby preparing theenergizing circuit including the pulsing contacts of relay 2041 for the vertical or primary switch magnet 223. Inthis circuit is included relay 22-1. Relay 222, in operating, also closes an energizing circuit for relay 257 which may be traced as follows: ground, lettalternate contacts or".

relay 222, outer right normal contacts of relay 248, outer right normal contacts of relay 211 and winding of relay 257 to battery.

Relay 257 operates in this circuit for a purpose to be later described.

The next operation on the part of the operator, after having inserted plug 107 into jack 200 is to turn the dial 118 to the first digit of the wanted number. As the dial returns to normal, the loop dialing circuit is interrupted a number of times corresponding to the digit selected and thereby causes the synchronous release of relay 204:. .This relay in turn loses the prepared circuit for the vertical magnet 223 which now also oper ates a corresponding number of times and in series with relay 224. It will be noted that relays 222 and are slow to release and although the circuits for these relays are alternately opened, they will be held operated during the pulsing. The circuit for operating relay 224 and magnet 223 can be traced from battery, winding of magnet 223,

winding of relay 224-, contacts 225 of relay 226, contacts 227 of relayv 222 and right normal contacts of relay 204 to ground.

When the selector took its first step due to the energization of magnet 223, the oilnormal switch 228 operated, thereby closing a circuit for the operation o1 relay 229 which an be traced as follows: battery, normal contacts of relay 208, contacts 230 of switch 228, winding of. relay 229, contacts 231 of relay 224 and to ground at the left alternate contacts of relay 222. In attracting its right-hand armature, relay 229 looks itself up in a circuit including the normal contacts of rotary magnet 232 and its own right-hand alternate contacts. Relay 229, in operating, also closes a short circuit path around the winding of relay 226 which can be traced from ground, lelt alternate contacts of relay 222, the right-hand terminal of the winding of relay 226 and from the left-hand terminal of this winding to ground at the right-hand alternate contacts of relay 229 to prevent this relay from operating at this time.

With each interruption of the dial contacts during the transmission of the first digit, the vertical magnet 223 will be energized and step the brushes to the desired level of the switch bank. Upon the cessation of the impulses and the release of relay 22 1-, which relay as stated held up during the pulsing, the circuit of the rotary magnet 232'is closed as follows: battery, winding of magnet 232, left alternate contacts of relay 229. contacts 233 of relay 22 i and to ground at the left-hand alternate contacts of relay The energization of the rotary magnet 232 causes the brushes to be moved into contact with the terminals of the first trun and by interrupting at its normal contacts the locking circuit for relay 229 pre v'iusly traced causes this relay to release which thus in. turn breaks the energizing circuit of magnet 232. The switch will, therefore, come to rest on this first trunk if it is idle that is, it no ground is present on the terminal S. Under these circumstances, the short circuit across the terminals of the winding of relay 226 will also be opened when relay 229 releases and when the armature oi? magnet 232 restores to normal, relay 226 will operate in the following circuit: ground, left alternate contacts of relay 222, winding of relay 226, normal contacts of magnet 232. winding of relay 229, contacts 230 of switch 238 and normal contacts of relay 203 to battery. Relay 226 operates in this circuit, but rel ay 229 which is marginal, will not operate at this time due to the high resistance introduced into the circuit by the winding of relay 226. i

it the first trunk on which the brushes laud i busy, its sleeve contacts 8 are grounded. In this case, relay 229 releases as before but relay 220 will not operate as it is still short-circuited, this time through its otvn contacts 23% to ground on the S terminal in stead of to ground over the right-hand alternate contacts of relay 229. When therefore the rotary magnet 232 releases its armature, .relay 229 will again energize, but this time to the ground on the S terminal whereupon the rotary magnet will be again energized .to step the brushes forward to the next trunk. The foregoing operations will be re peated until a non-busy trunk is reached.

W'hen relay 22loperated on the first pulse of the digit dialed, its contacts 237' were closed thereby completing a circuit for the energization ,ot relay 238 which can he lra: -ed as followsfbattery, Winding o'l relay 288, contacts 237 of relay 224i and to ground over the left alternate contacts of relay Relay 238, in operating. locked up independent of the contacts 237 of relay 224 in the following circuit: battery. Winding and inner right alternate contacts of relay 238, contacts 240 of relay 226 and to ground at the left alternate contacts of relay 22 Re lay 238, in operating, also opens the circuits for relays 212 and 24-1 and shunt"- condenser 24-2 of repeating coil 2 13 by resislance 2 so that relay'300 (Fig. in the conneaior associated with the trunk selected will thereilore operate when the tip and ring conductors are closed by the'operalion ol relay 226. It should be understood that additional selectors may be interposed biliffltll the connector and the selector shown in Fig.

2, depending on the capacity of the system, as is well known in the art.

When the brushes land on an idle trunk. relay 226 operates as before described and closes its left-hand contacts thereby extend ing the trunk through to the connector (Fig. Relay226, in operating, also opens at its contacts 225, the stepping circuit previously traced for the vertical magnet and in closing its contacts 235, transfers the holding circuit for relay 238, previously described, to the control. lead 308 completed to terminal 0. Relay 238 is, therefore, non

held ener ized over this control lead. through I b a I a circuit which may be traced ll'Olll ground at the left alternate contacts of relay 222, innerright alternate contacts oi relay 220, sleeve brush of the selector. terminal S, con ductor 306, contacts 307 of relay 30]. control lead 308, terminal C, the control brush, contacts 235 of relay 226, inner right alternate contacts and the winding of relay 238 to battery.

The seizure of the trunk extending to the connector completes as stated an energizing circuit for the pulsing relay 800 which now may be traced as follows: battery, lett hand Winding of relay 300, contacts 304; of relay 301, ring conductor 302, terminal 1%. corresponding selector brush, contacts 2+l5 of relay 226, contacts 239 of relay 204, contacts 24:7 of relay 2&8, lowerright winding of repeating coil 243, resistance 2%, contacts 250 of relay 238, upper right winding of re peating coil 213, contacts oi relay 248, contacts 25% of relay 220, a selector brush and corresponding terminal '1, conductor 303, contacts 805 of relay 301 and the righthand winding of relay 300 to ground. Ftclay 300 in energizing closes at its alternate contacts a circuit for relay 309 which may be traced from battery, rigl1t-l1and Winding of relay 300, alternate contacts of relay 300,

contacts 310 of relay 301 to ground. Relay 309, in operatin locks at its inner right alternate contacts to ground on control lead 308 over contacts 311 of relay 312. Relays sec and 309, in operating, open the circuit ol? the release magnet 313.

Tl. now the toll operator manipulates the dial in accordance with the tons and units tacts 316 of oil-normal switch ill? and windings of relay 318 and vertical magnet 314 to battery. The energization of .vertical magnet 31 i causes the lJIUSllQS of the connector switch to move one step oil. normal whereupon the oflmormal switch 317 operates and switches the impulse circuit of vertical magnet 31% over an alternate oil-normal contact through. the alternate contacts of slow to release relay 318, which relay operated in series with magnet 314 at the first impulse. Relay 318, in operating, also opens at its normal contacts the circuit oil rotary magnet 319. Relay 318 due to its slow to release character, holds operated during the transmission of the succeeding pulses. As the pulses continue, magnet 314: elevates the brushes to the desired level and upon the cessation of the impulses, relay 31.8 releases andtransfers the pulsing circuit from the vertical magnet to the rotary magnet 310. The return of the dial to normal in transmitting the last or unit digit impulses, causes the relay 300 to be released for each interruption of the dial contacts and thus cause the operation. of the rotary magnet 310 to move the switch brushes into engagen'ient with the desired line. Relay 320 in series With magnet 819 and energizes on the first impulse, but due to its SlOW to release charactor holds operated during the remainder of the pulses of the series. Relay 320,in

operating, opens at its inner normal contacts, the operating circuit for relay 312, prepares the busy test circuit by closing its contacts 322, and opens the hunting lead at its outer normal contacts.

As soon as relay 320 releases, at the end of the pulsing and if the called line is idle, a circuit is closed at contacts 321 of relay 320 for the operation of relay 301 which can be traced as follows: battery, throughthe usual cut-oil relay (not shown) associated with the called line, sleeve terminal 323, sleeve brush of the switch, contacts 321 of relay 320, contacts 324 of relay 325, contacts 326 of relay 312, contacts 327 of relay 301, left alternate contacts of relay 309, left-hand winding of relay 301, sleeve conductor 306, terminal S (Fig. 2) the sleeve brush of the selector, inner right alternate contacts of relay 226 and to ground at the left alternate contacts of relay 222. Relay 301 and the cut-off relay of the called line, operate in this circuit. Relay 301, in operating, removes ground at its contacts 307 from the control lead 308 which extends back to the selector, thereby causing the release thereat of relay 238. Relay 238, in releasing, closes at its left normal contacts, an obvious energizing circuit for relay 212, which relay, in operating, reverses and reduces the current flowing back over the trunk to the dial circuit of Fig. 1 by including resistances 214, 219 and 217 in the circuit and thereby causing the energization of polarized relay 120. This relay, in turn, causes relays 119, 116 and 109 to release. Relay 109 in turn disconnects the dial circuit fromthe trunk and connects the cord circuit thereto instead. lVhen relay 109 releases, supervisory relay 12a operates due to the fact that it is bridged across the tip and ring conductors of the cord circuit which is now con nected to the trunk and supplied with battel-y from the datum machine switching oflice. Relay 12 1, in operating, causes supervisory lamp 125 to lightas an indication to the operator that the line dialed. has been seized and that everything is in readinesstor her to ring.

' As before mentioned, the release of relay 233 was caused by the operation of relay 301 which removed ground from the control lead. However, when relay n38 retracts its inner right armature, it replaces ground on the control lead over the following circuit: ground, left alternate contacts of relay 222, outer right normal contacts of relay 2418, left alternate contacts of relay 257, inner left normal contacts of relay 211, inner rightiiorn'ial contacts of relay 238, contacts 235 of relay 220 to the control brush which is in contact.

with terminal (l of the control lead. This replacing of the ground on the control lead prevents relay 309 from releasing at this time. The operation of relay 301, in ad dit-ion to removing ground from the control lead as previously mentioned, also discon nects the tip and ring conductors 303 and 302 from the pulse relay 300 and extends them through the tip and ring brushes of the by operating ringing key 114, she thereby.

operates ring-up relay 258 (Fig. 2) which relay, in operating, closes an obvious energizing circuit for relay 248. Relay 24-8, in operating, opens at its outer right normal contacts, the ground connection previously traced for the control lead thereby causing relay 309 (Fi 3) to release. This connects ringing current to the called line in the following circuit: generator, interrupter 343, contacts 328 of relay 301, left-hand winding of relay 309, contacts 329 of relay 309, contacts 330 of relay 312 and over the ring brush and terminal of the connector to one side of the called line, the other side of the line being grounded at the outer right alternate contacts 340 of relay 301 through the top brush and terminal of the connector, middle right normal contacts 333 of relay 312, third outer normal contacts 342 of relay 309, outer right alternate contacts 340 of relay 301 to ground. Th s ringing circuit is intermittently interrupted by interrupter 343 until the called subscribe-r answers, when the removing of the receiver from the rack causes direct current, superimposed on the ringing generator as is the usual practice, to flow in the left-hand winding of relay 309 which of course is not responsive to the ringing alternating current. This direct current is suilicient to again 0perate this relay, which now in operating disconnects the ringing current from the line and again locks up to the control lead.

is brought out in the statement of the invention, the contact springs of ring-up relay 258 are so adjusted that the inner springs are of very light tension and are closed on the first pulse of the ringing current, thereby preparing a locking circuit for ringing relay 243 which is completed when this relay operates. The outer contacts of relay 258,

however, have a heavier tension and do not close until the ringing current has fully magnetized the core of the relay. This phase of the invention is a decided improvement over the usual ring-up relay arrangement which liable to permit the ringing relay 248 to chatter, in casethe ringing current received over the trunk is attenuated tosuch an extent as to just barely operate the usual ring-up relay which would then tend to follow the 16 cycle ringing current pulses. In this arrangement on the other hand the ring-uprelay would under such circumstances, as soon as it has once attracted its heavy tension conarmature, again connects ground to the con trol lead independent of ringing relay 248. This connection can be traced from ground, left alternate contacts of relay 222, left normal contacts of relay 257, inner left normal contacts of relay 211, inner right normal contacts of relay 238, contacts 235 of relay 226, the control brush and corresponding terminal G of the control-lead 308. Relay 257 is slow to release so that relay 309 of the connector circuit will release first. Therefore, it will benoted that when relay 309 is operated the second time as described above when the subscriber removes his receiver from the hook in answer to the ring ing, it will immediately find ground on the control lead and thus be maintained locked up independent of the fact that the toll operator may still have the ringing key depressed and consequently relay 2 18 operated.

If, for some reason or other it should become necessary to recall the wanted sub scriber while he is still connected to the line, this may be done by having the toll operator depress the ringing key 114- and all operations would be the same as hereinbefore described up to and including the operation of relay 248, as vthe called subscribers re-, ceiverwill in this case be off the hook when rela 248 oaerates and the re-rin 'in our rent will be applied to the wanted subscriber through the operation of relay 211. Relay 211 is operated over an obvious circuit closed by the operation of relay 241. That is, relay 241 operates when the subscribers loop iscompleted over a circuit as follows: Battery, winding. of relay 24:1, middle righthand normal contacts 255 or relay 238, righthand lower winding of repeating current 243, and back-through the subscribers loop to the upper right-hand winding of this coil to'ground at the outer normal contacts 250 of relay 238. Relay 211, in operating, connects ground at its inner alternate contacts to the control lead in the following circuit; ground, inner left alternate contacts of relay 211, inner right normal contacts of relay 238, contacts 235 of relay 226, control brush and terminal C of the control lead 308, thereby preventing relay 309 from releasing. Relay 211, in operating, thus connects uninterrupted ringing current through the springs of relay 2 18 for transmission oyera'n obvious path tothe called line.

ring-up relay It will be noted that when the toll opeif ator decides to re-ring, relay 211 is already operated before relay 248 becomes operated and consemiently, when relay2418 does operate, ringing current from the scare 1 at the inner right-hand armature and alternate contact of the relay 211 is already connected through. to the middle left-hand trunk line, so that no (.lisagreeable clicks orother disturbances that would ordinarily occur in circuits of this type during the change-over from the talking leads to the ringing source, will be present in the system designed in accordance with this invention.

In case the polarized 135 cycle relay 121 in the composite ringer associated with the calling toll should operate for any reason either falsely or due to the distant toll operator rc-ringing the toll operator, the 16 cycle current applied at the springs of relay 126 will he suiliciently limited, either by the high resistance 12? or in any other suit able manner, so as to be incapable of operating the ring-up relay 258 although it is sutlicient to operate the supervisory relay 104i of the toll operators cord circuit.

In case the end of the toll cord is associated with a non-composited toll line such as L and the voltage of the ringing current measured across the terminals of ring-up relay 258 is such that this relaybarely op crates, relay 248 will not follow the ringing current causing chatter due to the assembly and adjustment of the contact springs of relays 258 and EMS. As before mentioned, the inner springs of relay 258 are sullicieutly flexible to close their contacts on very weak ringing current impulses, thereby preparing a locking circuit for relay 248, but due to the still adjustment of the outer springs of relay 258, these contacts will not be closed to operate relay 248 to lock it up unless the ringing current applied to relay 258 is of a certain value. It will, therefore, be noted that relay 248 cannot chatter in any event as it is not operated unless the ringing current is strong enough to fully operate the On the other hand if relay 248 is once energizechit locks up un der control of the flexible contact springs of relay 258 which will remain closed througln out the ringing on any current value which is sutliciently strong to close the stiller springs of this relay.

In connection with the selection of subtill l l la'i llci scribers lines by the operation of the rotary magnet 319 in response to the unit digit impulses the connector circuit shown in Fig. 3 is also designed to hunt automatically for an idle trunk of a group of trunks leading to a P. l3. In the case, therefore, where the wanted subscriber is located at a P. B. X. and the first trunk selected leading to this exchange is bu there will he ground on the sleeve and luiinting terminals of that trunk. It should he noted that in accordance with this invention the sleeve and hunting fierininals of the group of trunks leading to the P. B. X. except the in LA til] -circuit ind-i,

corresponding terminals of the last trunk are stra) )Gfil together. As shown in F 3 l a o the terminals of three P. 5. X. trunks are shown, two of which have their sleeve and ture and front contact of relay 301, inner left-hand armature and back contact 3536 of relay 3. .2, inner right hand armature and front contact of relay'325, middle right hand armature and back contact 321 of re 320, sleeve brush S and the correspondin terminal through the strap from this ter ininal to the hunting terminal. which will, therefore, also be supplied with ground from relay 301. The ground on the sleeve terminal of this trunk, therefore, cause. relay .325 to be operatet when the connector lands its brushes onthe tern 'nals of this P. B. X. trunk over the following circuit: Battery, finding of relay contacts of relay 32 0 tothe sleeve terminal. This relay now loclis up over the following car cult: Batter iiiltllllg0f relay 325, fifth .ture and heel: contact of r lay 30L, lorerand armature and front cinitact of relay .325, contacts 351 of relay 31.52 to the sleeve *fEIllll il This locking endent of the contacts of relay ilOr [is now relay 325 operates and relayBQO rel er the last interruption of the steppin circuit for the rotary mag net 319a circuit is thereby closed for relay due to the ground on the hunting leer as follows: Battery, winding of? relay 356, armature and back contact of rotaryinagnet Z319, inner left-hand armature and hack contact of relay 336, outer right-hand armature and front coinactof relay 325, inner rigl'ithand armature and back contact of relay 320, outer right-hand. armature and back contact of relay 312, middle right-hand armagnet 319 at its outer left-hand: armature and front contact to ground at contacts 311' of relay 2H2 from the control. lead 808...

Rotary magnet 319 in energizing steps. the

brushes of the connector to the terminals of. the next P. B. X. trunlr.

This circuit. for energizing magnet 319 may be traced as follows: Battery, winding of relay 319, out-; or left-hand armature and front contact of relay 836, contact 311 of'relay 312 to ground on the control lead 308. The rotary magnet 2-319 as stated controls the circuit for relay 336, which now is released and this relay in turn causes the release of magnet 319.

if this next trunk is alsowbusy, the opera tions described aboveare repeated, but if ity is idle, there will be no ground on either; the sleeve nor hunting terminals andrelay 325, therefore, releases to close the circuit for relay 801, which operates and starts the various operations, resulting finally in the ringing of the connected P. B. X. operator in the same manner as for an ordinary subscriher hercinhefore ClGSCTlbGCh On the other hand, if the next ternnnals to which thebrushes land are associated with the last trunk in the group leading to this particular P. B, X, and this trunk is busy,1t.

becomes necessary to prevent the connector from operating further and bring the brushes thereof into connection with the first trunk of the next succeeding group of. trunks or the nextsubscrlbers line,

the case may be and also to cause the.

connector to give a busy signal to thetoll operator, an indication that all trunks of this particular 1 P). X are engaged.

this case relay 312 will operate as the sleeve and hunting terminals of this last trunk are not connected together and consequently there will be. no ground on the huntingterniinal but onl on the sleeve terminal. Relay 312 is operated over a circuit as follows: Battery, winding of relay, S36, armature and back contact of rotary magnet 319, inner left-hand armature and back contact of relay 336, outer righthand armature and front contact of relay 32 nner right-hand arnia ture and back contact of relay 820, winding of relay 312, contacts 351' of relay 312. top

ground on the sleeve terminal S. Relay 326 does not operate in series with relayf312 as it is marginal in its. operation. The .op-;

eration of relay SlQtraHsfers the holding circuit for relay 309 from. the control lead tothe sleeve lead 306 at its outer left-hand armature and also closes an operating cirill cuit for relay 301 as follows: From battery, through relays 330 and 312, inner left-hand armature'and iront contact of relay 812, contacts 327 of relay 301, left-hand armature and front contact of relay 309, left-hand winding of relay 301 to ground on the sleeve lead 306. Relay 801 in operating provides a locking circuit for itself as follows: Battery,winding of rotary magnet 319, winding of relay 320, armature and back contact of relay 318, upper alternate contacts of oil-normal contact springs 317, right-hand windingoi' relay 301, inner right-hand armature and front contact of relay 301 to ground on the sleeve lead 300. Relay 301 in operating removes ground from the control lead 308 at its second right-hand armature andfront contact 307", to complete the operations as will be hereinafter described. Relay 301 also completes the connection of leads 302 and 303 at its left-hand armature and front contacts to relay 312, which it will be noted is held upby ground trom coin tacts of relay 301. Busy flash signals are now sent tothe toll operator in the follow ingmanner.

As previously explained, ground is taken off the control lead 308and consequently relay 238 is permitted to release. The release of this relay closes the circuit for relay 2&1 to ring lead 302, and when the interrupter 350 now interrupts the circuit for relay 241 and consequently also the circuit for relay 211. Relay 211 being intermittently operated removes and replaces battery on the trunk leading to the toll operators circuit, and it will be seen that relay 212 will also be operated when relay 2238 re leases and the reversal of battery by this relay 312 will as hereinbefore described cause the operation of the signal 225 at the toll operators position, and consequently the interruptions as caused-by the interrupter 350 will cause the signal to flash and in this manner notify the operator that the wanted subscribers line, or as in this case that all the-PCB. X. operators trunks, are busy.

Similar conditions will exist when the wanted subscribers line is in communication with the toll operator and the subscriber decides to recall the operator, at which'time the manipulations otthe switchhook will alternately operate and release relay 241 and consequently cause lamp 125 to flash to indi cate this condition to the toll operator. In releasing the connection, replacing of the subscribers receiver on the hook will light lamp 125 steadily as hereinbelore described and the toll operator may then remove plug 107 from jack 200, thus releasingthe various relays in the selector including relay 204,which results in the'operation of the releasingymagnet 208, over an obvious circuitthrough-the right-hand armature and baclr contact of relay 222. The circuit for the release magnet 208 opens at the off-non mal contacts 228 when the switch has returned to normal. The release of the connector takes place when the release magnet 313 is operated on the release of the relay 309 which is due to the removal of the ground from, the control lead 308. The cir cuit for the release magnet 330 may be traced as follows: Battery, winding of magnet 313, off-normal contacts 317, outer armature and back contact of relay 309, armature and back contact oi'xrelay 300, upper right-hand armature and back contact 310 of relay 301 to ground. This circuit for the release magnet 313 will open at the oltnormal contacts 317 when the connector has returned to nor mal.

lVhat is claimed is:

l. A marginal device for retransmitting ringing currents comprising a relay having a slow-releasing armature responsive to weak currents, and a quick-acting armature responsive to strong currents, and a second relay responsive for its initial energization to the operation of said quick-acting armature and for its continued energization responsive to said slow-releasing armature.

2. A relaying device for retransmitting ringing current only above a certain predetermined value comprising a relay having a slow-1'eleasin armature responsive to weak currents, an a quick-acting armature rcsponsive only to strong currents and a second relay for transmitting ringing current" responsive for its initial energization to the said quick-acting armature of said first relay and responslve ior 1ts continued energization to said "slow-releasing armature of said first relay.

3; A marglnal device responsive toalter nating current signals above a certain value comprising a relay having two armature springs of difierent stiffness and corresponding normally open contacts associated therewith, the operatlng characteristics of the relay being such that the weakest spring rcmains closed with its contact longer than the other spring with itscontact after the energizing current has ceased to flow in the winding of said relay, a second slowtooperate relay having an ope 'ating circuit controlled by the stiffer spring and its contact, and a holding circuit controlled by the weaker spring and its contact, the operating characteristics of the two relays being such that it the operating alternating current maintains the stiffer spring operated for a certain period during a half-wave of current to cause the second relay to become operated, said second relay will remain operated continuously as long as alternating current is applied.

4. In a telephone system, incoming lines,

outgoing trunks and subscribers lines, an

operators position and a cord circuit thereat for connecting the incoming line with an outgoing trunk, automatic switching means for extending a connected trunk to a subcult and a connected trunk, signaling means in the operators cord circuit responsive to said alternating current, means in said cord circuit for applying alternating current of a certain other value to the connected trunk, and signaling means in said trunks responsive to the alternating current signals of the last mentioned value only for signaling a connected subscriber.

5. In a telephone system, subscribers lines, an operators position, a source of ringing current, means for controlling the application of ringing current from said source to a subscr bers line comprising a relay having a Winding and normally closed contactsin the circuit from the source to the subscribers line, and another Winding for the locking of the relay when operated to prevent the application of ringing current through the first mentioned winding, and means controlled by the operation thereof for the release of said relay for the application of ringing current and for the locking up of the relaywhen it again operates to cut off the rmging current in response to the removal of the subscribers receiver from the hook.

6. In a telephone system, subscribers lines, a source of ringing current, means for controlling the operation and removal of ringing current from said source to a subscribers line comprising a relay having a winding and a contact in the circuit from the source to the subscribers line, another Winding included in a circuit for holding said relay operated to prevent the application of ringing current, means for controlling said second circuit to release said relay for the application of ringing current, means for operating said relay to discontinue the application of ringing current in response to the subscriber removing the receiver from the hook, and means for con trolling said second circuit to cause the lookless of the condition set up to apply ringing current.

In Witness whereof, I hereunto subscribe ing of the relayafter once operated regard- 

